But that's not how the justice system works. The prosecution has to make its case for why someone's guilty, and to which degree they're culpable, and the defense has to make a case for why they're not guilty, or to which degree they're culpable. They're wouldn't even be a trial if someone hadn't suspected you of being culpable for a crime.
If Seal Team Six had the opportunity to arrest bin Laden rather than kill him, I bet they would have--but like any law enforcement or military raid, the lives of the police or soldiers takes precedence; if they can't safely apprehend someone, or if they believe a suspect has or will draw a weapon and it's likely someone will be killed, they'll shoot first to defend themselves.